Dielectric medium



Patented Feb. 9, 1937' PATENT OFFICE 2,070,268 nmnno'rmo mmmn "HughBryson Glass, Anniston, All assignor to Swann Research, Incorporated, a.corporation of Alabama N6 Drawing Application July 10, 1931, Serial g g2 Claims. This invention relates to new compounds having improveddielectric and insulating properties.

One object of this'invention is the provision of means whereby thephysical and electrical prop- ,5 erties of chlorinated diarylcompositions may be It) In the design of electrical condensers orcapacitors for various purposes such as radio, alterhating current motorand various other uses, it

is particularly advantageous, in order to confine the apparatus in assmall a space as possible to use as an impregnant a dielectric having ashigh a dielectric constant as practicable.

Condensers or capacitors usually consist of alternate layers of conductg and non-conducting material, the latter usu ly being paper. .Al- 20ternate conducting plates during operation are charged to a differenceof electrical potential and are connected to separate terminals. The'ill have been found useful for this purpose, these electrical devicessuch as condensers can be materially improved by the use of certainchlorinatedhigh boiling diary] compounds either alone or admixed withchlorinated diphenyl. The high boiling compounds which vI prefer toemploy are produced as a by-product during the thermal synthesis ofdiphenyl from benzol. I have also discovered that the density of theresulting chlorinated product containing the high boiling compounds isappreciably lower than that of the chlorinated diphenyl itself, thelowerdensity being advantageous in decreasing the weight of materialutilized and hence, the weight of the finished condenser. a

The composition obtained by my invention may also be used alone ortogether with other ingre-. dients as a cooling medium for transformers,switches and-other electrical devices where insulating oils are commonlyused, and which have differ in the production of my improved compositionare rather diflicult to identify chemically. They are, as far as is nowknown, mainly composed of the hydrocarbons, ortho and para diphenylbenzene and hence are related chemically and struc- 5 turally todiphenyl. The. origin of these hydrocarbons is similar to that ofdiphenyl, i. e., they are .produced by the pyrolysis of benzol and areseparated from the pyrolysis product by distillation. a

Due to the appreciably higher boiling point possessed by these over thatof diphenyl itself it is customary, when making a separation of thepyrolysis productobtainedfrom benzene, to distill oil a technicaldiphenyl fraction between temperatures of 250x150 270.C., at atmosphericpressure. The residue or high boiling compounds remaining behind in thedistillation flask may be employed as such for the practice of'thisinvention, however, it is desirable to further distill these highboiling compounds. In doing so the temperature may be raised to 390 to400 C.,' and the high boiling fraction is thus divided into two parts.and known as distilled high boiling com pounds" and still bottoms. Thelast fraction or still bottoms thus obtained consists of some very highboiling compounds together with tar and carbon. j

In the preparation of my improved dielectric I prefer to mix togethervarying proportions of diphenyl together with the kdistilledhigh boilingcompounds obtained as above and chlorinate the mixture by passing inchlorine gas. Rapid and eflicient chlorination can be effected by theaddition of a small amount of iron or iron chloride to the mixture ofhydrocarbons' when the'chlorination has reached the desired degree theproduct is distilled preferably in vacua until it' has .almostcompletely distilled overs Yields on distillation in the neighborhood of95% 40' may be expected. Considerable benefit is obtained by theaddition of small amounts of lime 'to the distilling flask, whichaddition serves to prevent traces of iron chloride or hydrochloric acidfrom coming over during distillation, thus yielding a lighter coloredproduct of considerablybetter electrical resistivity. g

In the application of my invention to metallic foil condensers I maybuild the pack of alternate sheets of metallic foil and! paper. The packis then carefully dried preferably in a vacuum and while still hot "andin-the vacuum impregnator my improved dielectric insulating liquid isadmitted. Penetration of the dielectric liquid into the interior of thepackmay be aided somewhat by the application of pressure on the liquidimpregnant after sufficient time has been given to .expell most of theair by the vacuum treatment. By choosing a composition of suitableviscosity and correctly determining'the time of impregnation by trial asatisfactory uniform penetration may be had.

The composition and properties of my new composition are illustratedinthe following Table I. By way of comparison the properties of twosamples of chlorinated diphenyl are included in this table.

- Table I Hydrocarbon compositions Properties of dielectric Dis- 'Dielectric tilled Viscosity Specific Dihigh 11 33 sec. Saygravity 3332?phenyl boiling wntem bolt at at a (10m com- 210 F. 65l65 C.

pounds eye es) Percent Percent Percent 100 23. 9 63 1.251 4. 35 0 10040. 3 290 1. 405 4. 98 80 2c 41. 2 35. 7 1. 352 4. 87 80 20 52. 2 47. 5L 490 4. 56 50 50 42. 0 48. 8 L 383 4. 84 50 50 36.4 40.8 1.324 4.89

Properties of chlorinated diphenyl The possibilities of the inventionwill be apparent from the above table.

Among other things it will be apparent that if "a dielectric of lowspecific gravity is desired it is preferable to use the distilled highboiling compounds without admixture of diphenyl.

By comparing compositions 1 and 7 in the above table it will be seenthat in this manner a decrease of 17.8% in specific gravity is obtainedwithout a' sacrifice in the dielectric properties.

If 20% of distilled high boiling compounds is admixed with 80% ofdiphenyl and the mixture chlorinated to a viscosity of 47.5 seconds, thedielectric constant of the distilled product will have increased 0.26unit over that of diphenyl,

'an increase of over 6%. Compare compositions that the dielectricconstant is important.

While I have described my invention n several forms, it will be obviousto those skilled in the art that it is not so limited, but issusceptible of various other changes and modifications without departingfrom -the'spi'rit thereof, and I desire,

therefore, that only such limitations shall be placed thereupon as areimposed by the prior art or as are specificalrfiset forth in theappended claims.

What I claim is:

1. A dielectric medium comprising a chlorinated mixture of diphenyl andcomplex hydrocarbons having a higher boiling point than diphenyl andproduced in the pyrolysis of benzol,

said mixture having a chlorine content up to 52.2% and the proportion ofcomplex hydrocarbons therein to diphenyl varying from to 2. A dielectricmedium comprising chlorinated complex hydrocarbons mixed-withchlorinated diphenyl, said complex hydrocarbons having a boiling pointabove that of diphenyl and having been produced'by the pyrolysis ofbenzol, said chlorinated mixture of hydrocarbons and diphen ylcontaining up to 50% of chlorinated diphenyl, and the chlorinatedmixture having a. Saybolt viscosity between 40 and 290 seconds at 210 F.

HUGH BRYSON GLASS.

